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United States Patent |
5,150,102
|
Takashima
|
September 22, 1992
|
Machining fluid temperature deviation alarm
Abstract
A machining fluid temperature deviation alarm device is attached to an
electrical discharge machining device which, having a temperature sensor
(S1) for machining fluid temperature detection and a cooler (2) for
machining fluid cooling, controls the cooler in response to a temperature
sensor output signal, thereby controlling the machining fluid temperature
within an allowable range. The alarm device employs a second temperature
sensor (S2) for determining whether the machining fluid temperature is
within a predetermined temperature range set by means of a second setter
(5) and encompassing the allowable machining fluid temperature range. In
response to an output signal from the second temperature sensor,
indicative of a deviation of the machining fluid temperature from the
predetermined temperature range, a numerical control device (3) causes a
CRT display unit (6) to display a temperature deviation message, and stops
the operation of the electrical discharge machining device, thereby
preventing lowering of machining accuracy, fluctuation of machining speed,
and unstable electrical discharge machining that are attributable to the
deviation of the machining fluid temperature.
Inventors:
|
Takashima; Hidenori (Kamakura, JP)
|
Assignee:
|
Fanuc Ltd (Minamitsuru, JP)
|
Appl. No.:
|
499441 |
Filed:
|
June 22, 1990 |
PCT Filed:
|
October 19, 1989
|
PCT NO:
|
PCT/JP89/01074
|
371 Date:
|
June 22, 1990
|
102(e) Date:
|
June 22, 1990
|
PCT PUB.NO.:
|
WO90/04479 |
PCT PUB. Date:
|
May 3, 1990 |
Foreign Application Priority Data
| Oct 27, 1988[JP] | 63-269538 |
Current U.S. Class: |
340/584; 137/334; 137/551; 165/11.1; 340/593; 340/596; 340/679; 340/680 |
Intern'l Class: |
G08B 017/06 |
Field of Search: |
340/584,596,680,679,593
137/334,551
165/11.1,14
75/10.12,10.1
|
References Cited
U.S. Patent Documents
3927571 | Dec., 1975 | Athey | 340/595.
|
Primary Examiner: Swann, III; Glen R.
Attorney, Agent or Firm: Staas & Halsey
Claims
I claim:
1. In an electrical discharge machining device in which a machining fluid
temperature adjuster is controlled so that a monitored machining fluid
temperature is within an allowable temperature range, in response to an
output signal of a temperature sensor indicative of whether the machining
fluid temperature is within said allowable temperature range, a machining
fluid temperature deviation alarm device, comprising:
a setter for setting a predetermined temperature range encompassing said
allowable temperature range;
a second temperature sensor provided independently of said temperature
sensor and adapted to monitor said machining fluid temperature, determine
whether said monitored machining fluid temperature is within said
predetermined temperature range, and deliver a signal indicative of the
result of said determination; and
alarm means for giving an alarm in response to the output signal of said
second temperature sensor, indicative of a deviation of said monitored
machining fluid temperature from said predetermined temperature range.
2. A machining fluid temperature deviation alarm device according to claim
1, further comprising halt means for stopping the operation of said
electrical discharge machining device in response to said output signal of
said second temperature sensor, indicative of the deviation of said
monitored machining fluid temperature from said predetermined temperature
range.
3. A machining fluid temperature deviation alarm device according to claim
1, wherein said machining fluid temperature deviation alarm device is
attached to a wire-cut electrical discharge machining device as said
electrical discharge machine.
Description
TECHNICAL FIELD
The present invention relates to an alarm device attached to an electrical
discharge machine, and more particularly, to an alarm device adapted
automatically to give an alarm when the temperature of a machining fluid
deviates from a predetermined temperature range during electrical
discharge machining.
BACKGROUND ART
If the temperature of a machining fluid fluctuates during electrical
discharge machining, the specific resistance of the machining fluid and
hence, the machining speed, fluctuate, and also, the dimensions of a
workpiece vary. As a result, the stability of the electrical discharge
machining is ruined, and the machining accuracy is lowered.
Conventionally, therefore, when the machining fluid temperature detected
by means of a temperature sensor, such as a thermostat, exceeds an
allowable upper limit value, the operation of a cooler for cooling the
machining fluid is started. When the machining fluid temperature is lower
than an allowable lower limit value, the operation of the cooler is
stopped. Thus, the machining fluid temperature is controlled within a
predetermined range of temperature.
Even in an electrical discharge machine provided with such a machining
fluid temperature control system, however, if the cooler or the
temperature sensor goes wrong, or if the electrical discharge machining is
executed without connecting the cooler to the power supply, for example,
the machining fluid temperature deviates from the predetermined
temperature range, so that the aforementioned awkward situation is
entailed. Namely, the stability of the electrical discharge machining is
ruined if the machining fluid temperature rises too high, or the machining
fluid is frozen if it is excessively cooled, for example.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide a machining fluid
temperature deviation alarm device used in an electrical discharge machine
and adapted automatically to give an alarm when the machining fluid
temperature deviates from a predetermined temperature range during
electrical discharge machining.
In order to achieve the above object, according to the present invention,
there is provided a machining fluid temperature deviation alarm device
attached to an electrical discharge machine, in which a machining fluid
temperature adjuster is controlled so that a detected machining fluid
temperature is within an allowable temperature range, in response to an
output signal of a temperature sensor indicative of whether the machining
fluid temperature is within said allowable temperature range.
This alarm device comprises a setter for setting a predetermined
temperature range covering the allowable temperature range, a second
temperature sensor provided independently of the temperature sensor, and
alarm means. The second temperature sensor detects the machining fluid
temperature, determines whether the detected machining fluid temperature
is within the predetermined temperature range, and delivers a signal
indicative of the result of the determination. The alarm means gives an
alarm in response to the output signal of the second temperature sensor,
indicative of a deviation of the detected machining fluid temperature from
the predetermined temperature range.
Preferably, the machining fluid temperature deviation alarm device includes
halt means for stopping the operation of the electrical discharge machine
in response to the output signal of the second temperature sensor,
indicative of the deviation of the detected machining fluid temperature
from the predetermined temperature range.
According to the present invention, as described above, the alarm is given
when the machining fluid temperature deviates from the predetermined
temperature range which covers the allowable temperature range, due to
some trouble in the machining fluid temperature sensor or the machining
fluid temperature adjuster, or a failure to connect the temperature
adjuster to the power supply, and preferably, the operation of the
electrical discharge machine is stopped when the alarm is given. Thus,
lowering of machining accuracy, fluctuation of machining speed, and
unstable electrical discharge machining, which are attributable to the
offstate of the machining fluid temperature, can be prevented.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view showing the principal part of a wire-cut
electrical discharge machine furnished with a machining fluid temperature
deviation alarm device according to one embodiment of the present
invention; and
FIG. 2 is a diagram for illustrating the operation of the alarm device of
FIG. 1.
BEST MODE OF CARRYING OUT THE INVENTION
In FIG. 1, a wire-cut electrical discharge machine, furnished with a
machining fluid temperature deviation alarm device according to one
embodiment of the present invention, comprises a machining fluid tank 1
for storing a machining fluid, a machining fluid temperature adjuster
formed of, for example, a cooler 2 communicating with the machining fluid
tank 1 and adapted to cool the machining fluid, and a numerical control
device 3 including a display unit formed of, for example, a CRT display
unit 6, and used to control the operation of various parts of the
electrical discharge machine. The machining fluid tank 1 and the cooler 2
are arranged in a conventional machining fluid circulating system (not
shown) attached to the electrical discharge machine.
The electrical discharge machine further comprises first and second
temperature sensors S1 and S2, which include first and second probes S1-1
and S2-1, respectively, for machining fluid temperature detection located
at a predetermined height position in the machining fluid tank 1. The
first temperature sensor S1 is disposed in the cooler 2, along with a
first temperature setter 4 for setting the allowable range of the
machining fluid temperature, and is connected to the first temperature
setter 4 and a control unit (not shown) for controlling the operation of
the cooler 2 in response to the output of the sensor S1. The first
temperature sensor S1 serves to determine whether the actual value of the
machining fluid temperature detected by means of the probe S1-1 is within
the allowable temperature range, and delivers an output signal indicative
of the result of the determination to the control unit of the cooler 2.
Further, the second temperature sensor S2, which is connected to the
numerical control device 3 and a second temperature setter 5 for setting a
predetermined temperature range covering the aforesaid allowable
temperature range, serves to determine whether the actual value of the
machining fluid temperature detected by means of the probe S2-1 is within
the allowable temperature range, and deliver an output signal indicative
of the result of the determination to the numerical control device 3.
These elements 3, 5, 6, S2 and S2-1 constitute the machining fluid
temperature deviation alarm device.
Referring now to FIG. 2, the operation of the electrical discharge machine
with the machining fluid off-temperature alarm device of the
aforementioned construction will be described.
Before the start of the operation of the electrical discharge machine, an
operator sets an allowable upper limit value T1 and an allowable lower
limit value T2, which define the allowable range of the machining fluid
temperature T, in the first temperature setter 4. Also, an upper limit
value T3 greater than the value T1 by a first predetermined value and a
lower limit value T4 smaller than the value T2 by a second predetermined
value are set in the second temperature setter 5 (T4<T2<T1<T3). Namely, a
predetermined temperature range defined by the values T3 and T4 and
covering the allowable temperature range is set in the second temperature
setter 5. The first and second predetermined values associated with the
setting of the values T3 and T4 are determined in consideration of a
normal detection delay of the first temperature sensor S1, a normal
operation delay of the cooler 2, and the like.
After the start of the operation of the electrical discharge machine, the
machining fluid temperature T generally rises with the lapse of time.
During electrical discharge machining, the first temperature sensor S1 in
normal operation compares the actual value of the machining fluid
temperature T detected by means of the probe S1-1 with the values T1 and
T2 set in the first temperature setter 4, and delivers a signal indicative
of the result of this comparison to the control unit of the cooler 2.
Thus, the output signal of the first temperature sensor S1 is on its first
level when the machining fluid temperature T is within the allowable range
defined by the values T1 and T2, and on its second level when the
temperature T is off the allowable range. Likewise, the second temperature
sensor S2 compares the actual value of the machining fluid temperature T
detected by means of the probe S2-1 with the values T3 and T4 set in the
second temperature setter 5, and delivers a signal indicative of the
result of this comparison to the numerical control device 3. Thus, the
output signal of the second temperature sensor S2 is on its first level
when the machining fluid temperature T is within the predetermined range
defined by the values T3 and T4, and on its second level when the
temperature T is off the predetermined range.
If the machining fluid temperature T attains the allowable upper limit
value T1 so that the output signal of the first temperature sensor S1
changes from the first level to the second level, while the first
temperature sensor S1 and the cooler 2 are normally operating, the control
unit of the cooler 2 causes the cooler 2 to start operation. As a result,
the machining fluid is cooled, so that the machining fluid temperature T
lowers. Thus, as long as the detection delay of the first temperature
sensor S1 and the operation delay of the cooler 2 are normal, the
machining fluid temperature T never exceeds the upper limit value T3 set
in the second temperature setter 5. If the machining fluid temperature T
attains the allowable lower limit value T2 so that the output signal of
the first temperature sensor S1 changes from the second level to the first
level, thereafter, the cooler control unit stops the operation of the
cooler 2, so that the machining fluid temperature T rises. In consequence,
the machining fluid temperature T is never lower than the lower limit
value T4 set in the second temperature setter 5. Thus, when the first
temperature sensor S1 and the cooler 2 are in normal operation, the cooler
operation is on-off controlled in response to the output signal of the
sensor, so that the machining fluid temperature T is controlled within the
allowable range.
In case of abnormal operation of the first temperature sensor S1 or the
cooler 2, attributable to some trouble in the first temperature sensor S1
or the cooler 2 or a failure to connect the cooler 2 to the power supply,
the operation of the cooler 2 sometimes cannot be started even when the
machining fluid temperature T exceeds the allowable upper limit value T1,
or the cooler operation sometimes cannot be stopped even when the
temperature T is lower than the allowable lower limit value T.
If the machining fluid temperature T exceeds the predetermined upper limit
value T3 greater than the allowable upper limit value T1, due to such an
abnormal situation, the output signal of the second temperature sensor S2
changes from the first level to the second level. Namely, an alarm signal
is delivered from the sensor S2. In response to this alarm signal, the
numerical control device 3 causes the CRT display unit 6 to display a
message to the effect that the machining fluid temperature is off.
Preferably, the numerical control device 3 stops the operation of the
electrical discharge machine the moment the message is displayed.
Likewise, if the machining fluid temperature T becomes lower than the
predetermined lower limit value T4 smaller than the allowable lower limit
value T2, due to the abnormal situation, an alarm signal is delivered from
the second temperature sensor S2, so that an offstate message is
displayed, and the operation of the electrical discharge machine is
stopped.
The present invention is not limited to the embodiment described above, and
various modifications may be effected therein.
In the above embodiment, for example, the offstate message is displayed on
the display unit 6 controlled by the numerical control device 3 which
operates in response to the alarm signal from the second temperature
sensor S2 when the machining fluid temperature has deviated beyond the
allowable limits. Alternatively, however, the alarm signal may be supplied
to a lamp or buzzer after being amplified, without being supplied to the
numerical control device, so that an alarm is given by means of the lamp
or buzzer.
In the embodiment described above, moreover, the cooler 2 is used as the
machining fluid temperature adjuster. When the electrical discharge
machine is operated at a low open-air temperature, however, a heater may
be used as the machining fluid temperature adjuster. In this case, the
heater is turned on when the machining fluid temperature T attains the
allowable lower limit value T2, and is turned off when the allowable upper
limit value T1 is attained. If necessary, the electrical discharge machine
may be provided with both the cooler and the heater so that either of them
can be alternatively used.
Although the present invention is applied to the wire-cut electrical
discharge machine in the above embodiment, furthermore, it may be also
applied to electrical discharge machines of any other types.
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